1. Field of the Invention
The present invention relates to embroidery machine, and more particularly, to a presser foot drive structure for embroidery machine.
2. Description of the Related Art
As well known in the art, an industrial embroidery machine is a type of machine in which an embroidery frame fixing a sheet of fabric moves horizontally in x- and y-axial directions in order to embroider a desired pattern on the fabric, while a needle bar capable of sewing moves up and down. A sewing machine carries a sheet of fabric using a geared carriage to sew the fabric sheet. In contrast, the embroidery machine performs needlework while the embroidery frame, fixing the sheet of fabric, is carried in x- and y-axial directions. Accordingly, the precise and constant-speed movement of the embroidery frame has a close relationship with the quality of an embroidered pattern.
Thus, as a source of power for driving the needle bar of the embroidery machine in a vertical direction, a servo motor, an induction motor, the speed of which can be controlled, or the like is used. As a power source for carrying the embroidery frame in x- and y-axial directions, a stepping motor, which ensures good positioning and is easy to control, is typically used.
Generally, 12 to 24 sewing machines are connected with each other along one spindle in order to improve the productivity of embroidery machine. Since the sheet of fabric must be sewn with various colors of thread corresponding to an embroidery design, each sewing machine has 6 to 12 needle bars, which are equipped with different colors of thread.
These days, users are demanding the ability to easily input, copy and store embroidery designs while performing simple editing on the designs. The users are also demanding various functions, such as an automatic thread color change function, which is enabled according to an embroidery design, a trimming function of automatically cutting a thread when sewing is finished, a function of interrupting the operation of the machine and raising an alarm when a thread is inadvertently cut, an outage restoration function of restarting the embroidery machine when the sewing machine stops due to a power failure, and the like.
In addition to the above-mentioned attempts to improve embroidery quality, embroidery machine providers are adopting industrial computers or microcomputers to embroidery machines in order to meet user demands for multi-functional embroidery machine operation.
FIG. 1 is a perspective and partially expanded view illustrating an embroidery machine of the prior art, FIG. 2A is a perspective view illustrating a presser foot drive structure of the embroidery machine of the prior art, and FIG. 2B is an expanded view of part “A” of FIG. 2A. As shown in FIG. 1, a plurality of sewing heads is arranged in the front portion of a sewing machine 1, along the length thereof. In the front portion of a sewing arm 3 of each sewing head, there is provided a needle bar support case 4, which has a plurality of presser feet 5 acting as cloth pressing members.
The presser foot 5 serves to prevent a sheet of cloth to be sewn from coming loose when it is being sewn, and is provided so as to be vertically movable in cooperation with a needle bar (see the reference number 6 in FIG. 2A).
As shown in FIGS. 2A and 2B, the needle bar 6 acts as a guide shaft for the vertical movement of the presser foot 5. Presser foot supports 12 and 13 for mounting the presser foot 5 on the needle bar 6 in a vertically and reciprocally movable fashion are located in two places on the presser foot 5, such as the top end and the middle section of the presser foot 5, so that a needle bar holder 14 at the bottom end of the needle bar 6 does not pass through the middle section of the presser foot 5. This acts as a factor limiting the reduction of the stroke of the presser foot 5, that is, the distance between the upper dead point and the lower dead point of the presser foot 5.
The needle bar 6, which should always have a predetermined stroke length, vertically moves through the middle section of the presser foot 5. In the vertical movement of the presser foot 5, in order to avoid excessive interference with the needle bar holder 14, the stroke of the presser foot 5 should have a predetermined length that is determined according to the stroke of the needle bar 6.
When the presser foot 5 is located at the lower dead point 5, a predetermined gap is always maintained between a pressing portion, which presses the sheet of cloth to be sewn, and the middle section, which is slidably supported on the needle bar. Thus, in the presser foot 5 pressing portion, where the sheet of cloth to be sewn is pressed, supporting force for the needle bar 6 is unreliable. Since the needle bar 6 is assembled through the presser foot 5, it is complicated to replace the presser foot 5 when it is fractured or broken. It is also necessary to disassemble the needle bar 6 and reset the upper and lower dead points of the needle bar.